In many countries, the air-cushion transport vehicles find various applications in different branches of economy. A factor which restrains their further application is that a comparatively low reactive thrust is produced even by propulsion installations having substantial overall dimensions.
Known to the prior art is a propulsion installation of an air-cushion transport vehicle (cf., for example, British Pat. No. 1,306,687, Cl. B 60 V 1/00, issued on Feb. 14, 1973), comprising an axial fan provided with a wheel incorporating working blades installed in an annular duct.
For effecting the reversal of a reactive thrust, the annular duct is provided at its exit with rotatable shutters closing the exit section of the annular duct and guiding the air flow in the direction of reversal.
However, at closing of the exit section by the shutters, the aerodynamic resistance of the annular duct air channel increases, bringing about a respective rise in air pressure with the result that a separation of the air flow occurs on the working blades of the axial fan and the axial fan capacity is substantially reduced and consequently the produced thrust is decreased.
To prevent occurrence of such separation of the air flow on the working blades of the axial fan, use is made of low-loaded fan wheels having a small aerodynamic angle of the working blades.
However, such fan wheels produce a relatively low reactive thrust, i.e., they are of low productivity or efficiency. In this case, to increase the reactive thrust, the diameter of an axial fan wheel has to be enlarged and, consequently, the overall size of a propulsion installation has to be increased.
It is well known that the reactive thrust produced by the wheel of an axial fan, installed in an annular duct may be substantially increased at the expense of an additional ring slat installed at the entrance a certain distance ahead of the annular duct of a propulsion installation (cf., for example, British Pat. No. 1,532,442, Cl. B 63 H 1/28, 5/14, issued on Nov. 15, 1978).
Such a ring slat allows a greater amount of air to be passed through the entrance section into the annular duct. The ring slat contributes to elimination of the breakaway of the air flow on a radius internal surface of the entrance portion of the annular duct and increases the reactive thrust of a propulsion installation.
However, further increases in the thrust in such a propulsion installation, at the cost of increasing the aerodynamic load through enlarging the angle of the working blades of an axial fan, cannot be achieved in this case because of the air flow separation at the peripheral portion of the working blades, which occurs when the shutters are turned for reversal of the reactive thrust, as was heretofore described in considering operation of the axial fan in the annular duct.
Thus, the provision of a ring slat ahead of the annular duct in a propulsion installation does not ensure an increase of the reactive thrust of a propulsion installation of an air-cushion vehicle, to the full extent.